Darton Sleeves come semi-finished at 85mm so it leaves the sleeve thicker for higher boost applications.

Due to bore center you are very limited in the 2jz block with how thick a sleeve you can put in.

Making the bore at 85mm leaves the sleeve a little thicker so the sleeve has a little more structure since there isn’t a lot of support from the cast iron block.

You aren’t really losing any power in a boosted application by going down just 1mm, you can make it up by easily pushing more boost safely.